Before You Begin

Question #45929

Difficulty: 8/10 | 🟢 Free

The Question

A researcher applies a specific inhibitor of the malate-aspartate shuttle to an isolated, actively contracting red muscle fiber. Despite an abundant oxygen supply, the fiber rapidly exhibits premature fatigue. Which of the following best explains the physiological cascade leading to this fatigue?

Options

A.
Accumulation of cytosolic NADH forces the conversion of pyruvate to lactate to regenerate $NAD^+$ , leading to an ATP deficit that impairs $Na^+/K^+$ pumps and disrupts the resting membrane potential.
B.
Inhibition of the shuttle prevents the transport of pyruvate into the mitochondrial matrix, halting the Krebs cycle and causing an immediate failure of myosin cross-bridge detachment.
C.
The shuttle blockade depletes mitochondrial $FADH_2$ , stalling Complex II of the ETC and forcing the fiber to rely entirely on the creatine phosphate system.
D.
The inability to transport oxygen into the mitochondrial matrix shifts the fiber to white-muscle metabolism, causing lactic acid to directly denature troponin.

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Comparative_Analysis

Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.

Concepts Behind This Question

Shuttle System Impact|Red vs. White Muscle Fibers|Oxidative Phosphorylation

Why This Question Is Tricky

Common Mistakes

Conceptual Pivot: Distinguishing between the transport of carbon skeletons (pyruvate) and reducing equivalents (NADH).

A common misconception is that oxygen availability alone dictates aerobic respiration.

Students must synthesize that without the shuttle, cytosolic $NAD^+$ regeneration fails, forcing lactate production (a hallmark of white fibers) in red fibers, ultimately linking metabolic ATP deficit to the failure of active ion transport ( $Na^+/K^+$ pumps) required for muscle excitability.

Quick Facts About This Question

Question Information

Subject	Biology
Chapter	Respiration in Plants - Class 11
Concept	Shuttle System Impact
Difficulty	8
Cognitive Load	5
Target Solve Time	120 sec
Access	Free